The present invention relates to a device for compensating secondary moments of inertia in 5-cylinder in-line combustion engines with a uniform firing order 1-2-4-5-3. The device comprises first and second compensating mass means that are comprised of two compensating masses respectively and are provided in an area of respective ends of a crank shaft, with the first compensating mass means and the second compensating mass means having compensating shafts that are disposed parallel to the crank shaft. The first compensating mass means, viewed from a first crank throw of the crank shaft in a direction toward the fly wheel (showing a so-called star-like crank throw arrangement of the crank shaft), is rotated 180.degree. plus an angle in a rotational direction of the engine relative to the first crank throw and the second compensating mass means is arranged at an end of the crank shaft opposite the first compensating mass means and is rotated 180.degree. relative to the first compensating mass means. The two compensating masses of the respective first and second compensating mass means are in a torque connection with the crank shaft such that the two compensating masses respectively, rotate oppositely directed relative to one another with a double rotation speed of the crank shaft.
The publication by Professor Dr. Ing. Hussmann "Umdnick zur Vorlesung Maschinendynamik" provides the teaching for compensating free moments of inertia of a first, second and higher order. According to this publication the free moments of inertia disappear in engines having an even number of cylinders and a uniform firing order. On the other hand, in engines with an uneven number of cylinders and a uniform firing order a compensation for moments of inertia is necessary. The elimination of free moments of inertia of a second order may be achieved by providing two compensating shafts that are arranged in parallel to the crank shaft, whereby the compensating shafts rotate oppositely directed relative to one another with a double revolution speed of the crank shaft. The compensating shafts are provided with compensating masses at their free ends which are rotated about 180.degree. relative to one another. In order to maintain the phase relationship of the oppositely rotating compensating shafts relative to the crank shaft a torque connection between the two compensating shafts and the crank shaft is required. Viewed in the direction of the star-like arrangement of the crank throws of the crank shaft the compensating masses of one side which are arranged in parallel in their initial position must be rotated 180.degree.+.gamma. relative to a first crank throw of the crank shaft. The first crank throw in this respect is the one that is disposed at the end of the crank shaft opposite the fly wheel. The compensating shafts must be arranged in parallel to the crank shaft. It is known from U.S. Pat. No. 3,667,317 to provide oppositely rotating compensating masses for compensating secondary forces of inertia which are driven by a crank web via toothed wheels. The compensating masses in the given example of a four-cylinder engine is achieved by a crank web that is adjacent to a symmetry plane of the represented four-cylinder engine. With such a compensating device only forces due to inertia may be eliminated. Moments of inertia about the transverse axis may not be compensated in this manner.
It is known from DE-OS 36 15 695 to arrange the two compensating shafts, which are rotating oppositely to one another with the double revolution speed of the crank shaft, in an oil pan. The compensating shafts are disposed parallel to the crank shaft and are driven by the crank web via a toothed rim and intermeshing toothed wheels in order to maintain the revolution speed and phase relationship relative to the crank shaft. The toothed rim initially drives via a toothed wheel a first compensation shaft and then via a toothed wheel a second compensation shaft. The gear ratio of the toothed rim to the toothed wheels of the compensation shafts is 1:2. Since a four-cylinder engine is described in this reference no moments of inertia but only forces due to inertia will occur. In order to completely eliminate the secondary forces of inertia the compensating masses are provided only on one side of the compensating shafts in a symmetry plane A disadvantage of such a device must be seen in that the bearing within an oil pan is problematic with respect to the distance between pinion and toothed wheel which must be exactly adjusted. The sealing between the crank case and the oil pan flange is usually achieved via elastic sealings which, however, inadvertently result in a changing axis distances. A support in this manner can only represent a last resort when the support of the compensating shafts together with the compensating masses within other components of the engines is not possible.
The five-cylinder in-line combustion engine has free moments of inertia of a first and second order due to the crank shaft arrangement which is not symmetrical in the longitudinal direction. The load caused by these moments of inertia which is outwardly effective and increases with the square of the number of revolutions must be compensated by the engine suspension. Disturbing effects onto the environment are usually prevented by providing intermediate elastic components between the engine and the foundation. Due to respective adjustments it is possible to eliminate almost entirely the excitations due the inertia masses of the engine. This effect commonly known as insulation, i.e., reduction of the excitation forces on the foundation, will only result at over-critical adjustments when n.sub.err /n.sub.e &gt;.sqroot.2 and is the more effective the more the operation frequency n.sub.err deviates from the eigen frequency n.sub.e of the oscillating system, that is, the greater the distance between the operation point and the resonance location.
Concerning the foundation load the negative characteristics of the five-cylinder engine may be overcome by elastic support and optionally adjusted damping. Since the excitation forces in this case are primarily compensated by the engine and the adjacent gear unit and only fractionally by the foundation, high loads occur at the engine and the gear unit which may result in deformations, especially at the connection between the engine and the gear unit which is the soft spot of the oscillating system. Since the system due to its high eigen frequency in comparison to an elastic support is usually operated in an under critical range a certain safety distance to the resonance location must be maintained in order to prevent critical loads. Due to the secondary moments of inertia of a secondary order present in five-cylinder engines the usable range is rather limited and an increase in performance accompanied by heavier gear units results in a decrease of the eigen frequency which cause higher characteristic form amplitudes.
This results in a greater axial movement in the longitudinal compensation of the drive shaft which, at a high torque output, results in axial forces of a considerable amount and causes, besides uncomfortable axial oscillations, damages to the gear unit support.
It is therefore an object of the present invention to provide a device of the aforementioned kind for compensating secondary moments of inertia whereby the compensating shafts may be arranged within the crank case, even for existing combustion engines, without alterations to the crank case.